1. Field of the Invention
The present invention relates to an optical waveguide-type wavelength domain switch, which obviates shortcomings of conventional wavelength domain optical switches and waveguide-type wavelength selection switches.
2. Description of the Related Art
FIG. 14 shows a conventional wavelength domain optical switch 600. This wavelength domain optical switch 600 is composed of input/output optical fibers 601 to 606, a collimating lens array 610, a Wollaston prism 615 (composed of two triangular prisms 616, 617) for allowing independence of characteristics between horizontal polarization (y-polarization) and vertical polarization (x-polarization), a birefringent plate 620 for zeroing a phase difference between the horizontal polarization and the vertical polarization, a half-wave plate 625 (where only 626 is a half-wave plate and 627 has no effect on polarization), a concave mirror 630, a cylindrical lens 635, a grating 642 with a wedged prism 641, a prism 646 for bending light in a perpendicular direction, and an optical phase-modulating cell 645 called LCOS SLM (liquid crystal on silicon spatial light modulator).
FIG. 15 shows a conventional waveguide-type wavelength-selecting optical switch using an MEMS (micro electro mechanical system) micro mirror. Herein, its structure is such that five substrates with five waveguide-type multi/demultiplexing devices disposed on each substrate are stacked on top of each other. Use of the MEMS micro mirror allows a large reflection angle and therefore this structure, but applying this to a wavelength domain optical switch causes significant performance deterioration.
Refer to US patent publication No. 2006/67611 and U.S. Pat. No. 7,088,882, for example.
The wavelength domain optical switch in FIG. 14 has the following problems.
(1) Because of using the bulk grating, the dimensions of the bulk grating are large and difficult to reduce, though demultiplexing light by one grating is advantageous.
(2) Because of the complex optical system, each optical component and assembling are costly and difficult to reduce cost.
(3) The optical phase-modulating cell operates only for one polarization. For this, the prior art uses polarization diversity using Wollaston prism 615, birefringent plate 620 and half-wave plate 625 to thereby overcome polarization dependency. In this case, to equalize the optical length difference between 2 polarized waves, the birefringent plate 620 is used. However, the birefringent plate 620 has large dimensions, and therefore tends to be affected by refractive index variation with temperature and thermal expansion variation, leading to significant performance deterioration at 0° C.-65° C. environment temperatures in general optical communication device. Controlling the temperature of the entire optical system can reduce performance deterioration, but requires temperature-stabilizing apparatus, increasing dimensions and power consumption, and worsening practicality.
(4) In view of size of the collimating lens array, etc., because of a small reflection angle of the optical phase-modulating cell, the achievable number of input/output ports is limited, and difficult to increase.
The waveguide-type wavelength-selecting optical switch using the MEMS micro mirror in FIG. 15 has the following problems.
(1) Basically, plural waveguide-type multi/demultiplexing devices are disposed on one substrate. Use of the MEMS micro mirror allows a large reflection angle and therefore this structure, but applying this to a wavelength domain optical switch causes significant performance deterioration because of a small reflection angle of the optical phase-modulating cell.
(2) Because the waveguide-type multi/demultiplexing devices are disposed not obliquely but horizontally, reflection is caused at each optical component end face, causing property deterioration.
(3) Although stacking vertically for increasing the number of output ports, size is limited due to micro lens and waveguide-type multi/demultiplexing device substrate thickness, and high-density stacking is impossible. For this, an attempt to achieve multiple ports required in optical communications has difficulty reducing size, and enhancing performance.
(4) Because of demultiplexed wavelength variation due to temperature variation, the waveguide-type multi/demultiplexing devices cannot be used in optical communications, which is a fatal disadvantage.